Illuminated Brain Cells at Work

For that purpose research staff at the Carnegie Institution's Department of Plant Biology and Stanford University apply genetic nanotechnology using molecular sensors to view changes in brain chemical levels. The sensors alter their 3-dimensional form upon binding with the chemical, which is then visible via a process known as fluorescence resonance energy transfer, or FRET.

In a new study, the nanosensors were introduced into nerve cells to measure the release of the neurotransmitter glutamate. "The fluorescent imaging technique allows us to see living cells do their jobs live and in colour," explained Sakiko Okumoto, lead author of the study at Carnegie. "Understanding when and how glutamate is produced, secreted, reabsorbed, and metabolised in individual brain cells, in real time, will help researchers better understand disease processes and construct new drugs."

"FRET is like two musical tuning forks, which have the same tone," Okumoto continued. "If you excite one, it gives a characteristic tone. If you bring the second fork close to the first one, it will also start to give you a tone even though they do not touch. This is resonance energy transfer."

"We used a protein called ybeJ from the common bacterium E. coli. We first predicted the structure of this protein, and then placed the two fluorophores at specific positions on the binding protein," commented co-author Loren Looger.

"After fusion to the fluorescent proteins, we placed the sensor on the surface of rat hippocampal cells. The hippocampus is the part of the brain that is involved with emotional reactions, and it helps store learned information in memory. When neurons are activated, they secrete glutamate, and we could see this activity under the microscope by watching the colour change. We stimulated the neurons and watched them secrete glutamate in response. We also saw the removal of the glutamate as the neurons returned to normal ready to fire again," Loger added.